"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

From what we are told, large meteors or comets impact every few million years or so. Galaxies collide, supernovas happen and black holes swallow stars, and maybe solar systems with them.
Just like the continued warming and cooling of this planet over the eons - its going to happen no matter what we do.

Absolutely untrue. There is no physical reason why we can't deflect asteroids into safe orbits. There are many ways this could be achieved in theory and there are many people working on it practically. There are many natural disasters we are clueless about how to avoid, collisions with lumps of space rock are not one of them,

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001